This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to a Japanese Patent Application 2001-014074, filed on Jan. 23, 2001, the entire content of which is incorporated herein by reference.
1. Field of the Invention
This invention generally relates to a hydraulic brake apparatus. More particularly, this invention pertains to a vehicle hydraulic brake apparatus provided with a master cylinder, including a master piston and an auxiliary hydraulic pressure source, with the master piston being driven by power hydraulic pressure supplied from a auxiliary hydraulic pressure source via a linear solenoid valve unit.
2. Background of the Invention
Various vehicle hydraulic brake apparatus are known One type of vehicle hydraulic brake apparatus is disclosed in German Patent Laid-Open Publication No. 197 03 776A1. This hydraulic brake apparatus is provided with a master cylinder, a hydraulic pressure type boosting mechanism provided with a booster piston, a pump driven by an electric motor, and a pressure control valve for controlling a boosted hydraulic pressure applied to the booster piston. The hydraulic pressure discharged from the pump is controlled by the pressure control valve controlled by a proportioning solenoid mechanism so that various controls including a traction control and a vehicle stability control are performed. The pressure control valve, including the proportioning solenoid mechanism, corresponds to a linear solenoid valve.
However, in the above-described hydraulic brake apparatus, the desired controls may not be accurately performed due to errors associated with the solenoid mechanism. That is, fluctuations due to electric control of the solenoid mechanism and fluctuations due to mechanical components comprising the solenoid mechanism may have an affect on the proper performance of the control operations. Therefore, the characteristics of the solenoid mechanism need to be checked at a proper timing and should be corrected when needed.
Japanese Patent Laid-Open Publication No. 11-201314 discloses a correcting device for correcting characteristics of a solenoid valve. The characteristics of the solenoid valve may fluctuate due to fluctuations in the set load of a return spring. The correcting device is employed for compensating during the manufacturing process the fluctuating characteristics of the solenoid valve used, for example, for controlling the hydraulic pressure operating a vehicle automatic transmission. Therefore, according to this publication, an adjusting mechanism is not required to be mounted on the solenoid valve.
In the above-described Japanese publication, the fluid amount or fluid pressure is set to be controlled by the solenoid valve for the purpose of checking the characteristics of the solenoid valve. Electric current supplied to the solenoid valve is adjusted to match the fluid amount or the fluid pressure to a target fluid amount or a target fluid pressure to carry out the check, respectively. The difference between a predetermined electric current for design corresponding to the target fluid amount or the target fluid pressure for the check and the electric current actually required to meet the target fluid amount or the target fluid pressure is calculated based upon the relationship between the predetermined electric current and the target fluid amount or the target fluid pressure. Information for correcting the actually supplied electric current is calculated based upon the aforementioned difference and is memorized by a control device for controlling the solenoid valve.
Therefore, correction for the characteristics of the solenoid valve as a single unit can be effected as described above. That is, initial fluctuations of the solenoid valve as a single unit during the manufacturing stage can be corrected. However, the above-described Japanese publication does not disclose effecting correction for the characteristics of the solenoid valve mounted on the vehicle. Further, even if the correction for the characteristics of the solenoid valve as a single unit as described in the above Japanese publication is applied to the solenoid mechanism described in the German publication mentioned above, a desired effect may not be easily produced when brake control is performed during running of the vehicle.
That is, after the solenoid valve has been mounted on the vehicle, the characteristics of the solenoid valve may vary due to aging distortion of the solenoid valve itself, electric voltage characteristics, and the like. Further, temperature characteristics of the solenoid valve may vary due to a vehicle running condition such as a vehicle speed, an actuating condition of the solenoid valve, and the like. As a result, a desired brake control in the hydraulic brake apparatus described in aforementioned German publication may not be effected due to characteristic variations such as those mentioned above.
Accordingly, the disclosed vehicle hydraulic brake apparatus is still susceptible of certain improvements with respect to monitoring the characteristics of the solenoid valve already mounted on the hydraulic brake apparatus and correcting the characteristics of the solenoid valve when needed.
A need thus exists for the electric current actually supplied to the linear solenoid valve unit mounted on the vehicle to be accurately corrected so that predetermined brake controls can be accurately performed by the hydraulic brake apparatus.
According to one aspect, a hydraulic brake apparatus for a vehicle includes a brake operating member, a master cylinder including a master piston which is moved forward in response to a depressing operation of the brake operating member for pressurizing brake fluid in a reservoir and outputting a master cylinder hydraulic pressure to wheel brake cylinders mounted on respective vehicle wheels in response to the forward movement of the master piston, an auxiliary hydraulic pressure source for pressurizing the brake fluid in the reservoir to a predetermined pressure level and for outputting a power hydraulic pressure, master piston driving means for driving the master piston with the power hydraulic pressure outputted from the auxiliary hydraulic pressure source, and a linear solenoid valve unit for controlling the power hydraulic pressure supplied to the master piston driving means from the auxiliary hydraulic pressure source and for controlling a driving force applied to the master piston. A hydraulic pressure control valve device is disposed between the master cylinder and the wheel brake cylinders for controlling the master cylinder hydraulic pressure supplied to the wheel brake cylinders, a pressure sensor detects the master cylinder hydraulic pressure, and control means controls the linear solenoid valve unit and the hydraulic pressure control valve device. The control means includes comparing means for comparing the master cylinder hydraulic pressure detected by the pressure sensor with a predetermined reference hydraulic pressure when the linear solenoid valve unit is electrically excited under a condition that a communication between the master cylinder and the wheel brake cylinders is interrupted by the hydraulic pressure control valve device during a vehicle engine being activated and the brake operating member being not operated, and correcting means for correcting an electric current actually supplied to the linear solenoid valve unit in response to a comparison result by the comparing means. The control means further includes a correcting means for correcting electric current actually supplied to the linear solenoid valve unit in response to the result of the comparison performed by the comparing means.
Preferably, the control means also includes estimating means for estimating a temperature of the linear solenoid valve unit at a predetermined period based upon the excitation condition of the linear solenoid valve unit and the vehicle running condition. In this case, the electric current actually supplied to the linear solenoid valve unit is corrected by the correcting means when a variation of an estimated temperature per period continues to be less than a predetermined value for a predetermined period of time.
The hydraulic brake apparatus preferably also includes a brake operating detecting means for detecting whether or not the brake operating member is operated, with the control means terminating the correction of the electric current actually supplied to the linear solenoid valve unit when it is judged based upon a detected result by the brake operating detecting means that the brake operating member is operated.
The master piston driving means includes a regulating means connected to the auxiliary hydraulic pressure source and the reservoir for regulating the power hydraulic pressure outputted from the auxiliary hydraulic pressure source to a predetermined pressure level for driving the master piston by the regulated hydraulic pressure. Therefore, the linear solenoid valve unit controls the power hydraulic pressure supplied from the auxiliary hydraulic pressure source to the regulating means.
According to another aspect, a hydraulic brake apparatus for a vehicle includes a brake operating member, a master cylinder which pressurizes brake fluid in a reservoir through movement of a master piston and outputs a master cylinder hydraulic pressure to wheel brake cylinders in response to the movement of the master piston, an auxiliary hydraulic pressure source connected to the master cylinder to pressurize the brake fluid in the reservoir to a predetermined pressure level and output a power hydraulic pressure to drive the master piston, a linear solenoid valve unit disposed between the master cylinder and the auxiliary hydraulic pressure source to control the power hydraulic pressure supplied to the master cylinder from the auxiliary hydraulic pressure source and control a driving force applied to the master piston, a hydraulic pressure control valve device disposed between the master cylinder and the wheel brake cylinders for controlling the master cylinder hydraulic pressure supplied to the wheel brake cylinders, and a pressure sensor which detects the master cylinder hydraulic pressure. The apparatus is also provided with comparing means which compares the master cylinder hydraulic pressure detected by the pressure sensor with a predetermined reference hydraulic pressure during electrical excitation of the linear solenoid valve unit when communication between the master cylinder and the wheel brake cylinders is interrupted by the hydraulic pressure control valve device and while an engine of the vehicle is activated and the brake operating member is not operated, and correcting means which corrects electric current actually supplied to the linear solenoid valve unit in response to a result of the comparison performed by the comparing means.
Another aspect involves a method of controlling the supply of electric current to a linear solenoid valve unit in a vehicle hydraulic brake apparatus. The vehicle hydraulic brake apparatus includes a brake operating member, a master cylinder which pressurizes brake fluid in a reservoir through movement of a master piston and outputs a master cylinder hydraulic pressure to wheel brake cylinders mounted on vehicle wheels in response to the movement of the master piston, an auxiliary hydraulic pressure source which pressurizes the brake fluid in the reservoir to a predetermined pressure level and outputs a power hydraulic pressure to move the master piston, and a hydraulic pressure control valve device disposed between the master cylinder and the wheel brake cylinders for controlling the master cylinder hydraulic pressure supplied to the wheel brake cylinders. The linear solenoid valve unit controls the power hydraulic pressure supplied to the master cylinder from the auxiliary hydraulic pressure source to control the driving force applied to the master piston. The method involves detecting the master cylinder hydraulic pressure, comparing the detected master cylinder hydraulic pressure with a predetermined reference hydraulic pressure when the linear solenoid valve unit is electrically excited while communication between the master cylinder and the wheel brake cylinders is interrupted by the hydraulic pressure control valve device and while an engine of the vehicle is activated and the brake operating member is not operated, and correcting electric current actually supplied to the linear solenoid valve unit the comparison of the detected master cylinder hydraulic pressure with the predetermined reference hydraulic pressure.